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Q.
Tobacco plants resistant to nematode have been developed by introduction of DNA that produces
AIPMTAIPMT 2012Biotechnology and its Applications
Solution:
Many nematodes live in plants and animals including human beings. A nematode Meloidogyne incognita infests the roots of tobacco plants and causes a great reduction in yield. A novel strategy was adopted to prevent this infection that was based on the process of RNA interference (RNAi). RNA interference (RNAi) is the phenomenon of inhibiting activity of a gene by synthesis of RNA molecules complementary to the wRNA. The normal (in vivo synthesized) wRNA of a gene is said to be 'sense' because it carries the codons that are 'read' during translation. Normally, the complement to the wRNA 'sense' strand will not contain a sequence of codons that can be translated to produce a functional protein; thus, this complementary strand is called 'anti- sense RNA'. The anti-sense RNA and /wRNA molecules will anneal to form duplex RNA molecules (or double stranded RNA) and the duplex RNA molecules can not be translated. Thus, the presence of anti-sense RNA will block translation of the wRNA of the affected gene. In fact, recent evidence indicates that these RNA duplexes are often rapidly degraded in vivo. Using Agrobacterium vectors, nematode-specific anti-sense genes are introduced into the host plant. The introduction of DNA produces anti-sense RNA in the host cells. The transgenic host plants expresses anti-sense RNA. As in consequence, nematode infestation fails in the transgenic plants because the complementary anti- sense RNA forms a double stranded RNA (ds RNA) which interferes or blocks the translation and thus, silences the wRNA of the nematode. In such way, the transgenic plants get protected from the parasite.